1. Field of the Invention
The present invention relates to photography and particularly to new yellow dye image-forming couplers and to a method for forming yellow dye images by using the same.
2. Description of the Prior Art
The color developing method in color photography, namely, the formation of colored photographic images by the coupling of oxidized developers (oxidized aromatic primary amino developing agents) with couplers is well known. Among the yellow dye image-forming couplers used in said photographic process the so-called four-equivalent couplers have active methylene group which can couple with the oxidized aromatic primary amino developing agents to form yellow dye. Said four-equivalent couplers require reduction of four molecules of silver halide in order to form one molecule of dye by coupling with color developer. However, it is known that couplers in which one of hydrogen atoms in active methylene group is substituted with a substituent such as a halogen atom can also form the same dye as formed from unsubstituted couplers. In this case, said substituent (a splitting off group) is easily released on coupling and reduction of only two molecules of silver halide is required for formation of one molecule of dye. Therefore, these couplers are called two-equivalent couplers. Use of the two-equivalent couplers improves coupling reactivity over use of the four-equivalent couplers. Therefore, when the two-equivalent couplers are employed, obviating prolonged development makes it possible to provide color photographic light-sensitive materials suitable for rapid color developing process. Moreover, color photographic light-sensitive materials which contain two-equivalent coupler in silver halide emulsion require the silver halide in the amount of one-half that of silver halide required by the four-equivalent coupler and hence cost can be reduced. Furthermore, the emulsion layer can be made thinner to increase resolving power and sharpness of color image. Thus, the two-equivalent couplers are more desirable for color photography than the four-equivalent couplers. However, certain of the two-equivalent couplers do not have so high coupling reactivity or tend to produce color stains such as fog.